Frank Daly, chairman of Nama, said: "It is unfortunate, to say the least, that in some cases those making the allegations appear unconcerned about the reputational or commercial damage that their unsubstantiated allegations may cause to the organisation concerned or to any individuals that they may name.

"Often there are no consequences for them if their allegations prove to be without foundation, whereas the reputational damage to the organisation or individual may well be impossible to reverse."

Nama offered to publish full details of fees it paid over the sale of Project Eagle, a portfolio of loans linked to about 800 properties in Northern Ireland sold for £1.6 billion to US investor Cerberus.

Mr Daly added: "We have nothing to hide."

In a staunch defence of Nama's work the chairman also said it has raised its profit forecasts on the expected wind-up before 2020 from 1 billion euro to 1.75 billion euro.

On the Project Eagle deal, Nama said the buyers will make about 200 million euro gross profit.

Independent TD Mick Wallace, a former builder, first raised allegations about the sale by exposing a £7 million deposit in an offshore account which he said had been earmarked for a Northern Ireland politician.

Subsequently he said £45 million had been earmarked for "fixers" behind the scenes in the Project Eagle deal.

He also claimed some developers were being asked to buy back their loans from investors for half of what they originally borrowed.

As well as parliamentary probes in Stormont and Dublin, the UK's National Crime Agency is investigating the sale.

Nama met the NCA several weeks ago and Mr Daly said the criminal investigation is not concerned with the bank's role.

Nama insisted that its due diligence calculated that the Project Eagle portfolio was only worth 27% of what was originally borrowed.

Mr Daly said some of the assets may have been worth 50% but others were worth as little as 5%.

He defended the sale rather than attempting to hold on to the loans in the hope of a bounce in the Northern Ireland property market.

"I have little doubt that the commercial decision taken by the Nama board to dispose of the NI loan portfolio was the right one," Mr Daly said.

He told the Dail's Public Accounts Committee said it was "hearsay" to claim it was sold for less than it was worth.

She claimed the plug should have been pulled on the entire Project Eagle sale when it was discovered that a former member of Nama's Northern Ireland Advisory Committee, Frank Cushnahan, had been in contact with investment house Pimco, one of the last three bidders in the sale.

"I do not agree that the bidding process had been corrupt," Mr Daly said.

"I absolutely stand over the integrity of the process and stand over the fact that the taxpayer got value for money."

Mr Daly offered to get support from the Nama board to meet the Stormont finance committee in private after the agency was accused of stonewalling the Belfast assembly's inquiries into Project Eagle.

Daithi McKay, the chair of the Assembly Finance Committee in Belfast and a Sinn Fein MLA, said Nama's refusal to appear at a public hearing in Northern Ireland was deeply frustrating.

"Nama and others cannot continue to use the excuse of the ongoing criminal investigation as a reason for not coming before the committee," he said.

Sinn Fein's Martin McGuinness, the NI Deputy First Minister, said he would be willing to give evidence on his knowledge of the Project Eagle sale to the Public Accounts Committee.

Forty one files on the sale of Project Eagle were released by the Department of Finance at 9pm, sparking withering attacks from members of the Public Accounts Committee

One document showed Mr McGuinness had been listed as attending a teleconference on the sale of the Nama portfolio, with Finance Minister Michael Noonan and Democratic Unionist leader Peter Robinson, despite him saying previously that he had been "kept in the dark".

Independent TD Shane Ross said the publication of the documents was "deliberate and markedly politically divisive".

"it's quite shocking and quite extraordinary when these documents should be used at this stage when it's almost impossible to digest them," he said.

DUP MLA Simon Hamilton, a former finance minister in Stormont, said Mr McGuinness was "intimately involved in the discussions" around the Project Eagle sale.

"This evidence demonstrates beyond any doubt that Mr McGuinness's knowledge went far beyond what he has previously been prepared to admit," Mr Hamilton said.

"Last month he called into question the veracity of my account from that period and I would expect him to withdraw that statement and apologise as incontrovertible evidence has now come to light."

Later, Nama was pressed on allegations that Mr Cushnahan expected to be paid a success fee if Pimco won the auction.

"We were working on the basis of what Pimco told us in relation to Frank Cushnahan, what they told us he was to get out of this (Project Eagle sale)," Mr Daly said.

"There was potential there for huge reputational damage.

"But I don't believe he knew anything that was confidential."

Mr Daly added that he did not believe Mr Cushnahan had "any information that would have been of use to a bidder".

Nama revealed Cerberus, and failed bidder Fortress, would have spent 3.5m euro each on due diligence, with hundreds of people working on data related to the assets, before making a bid.

Cerberus nailed the bid offering £1.241 billion when the reserve price was £1.24, while Fortress came in at £1.1 billion.

Mr Daly dismissed suggestions that the winning bid was so close to the mark because the investment house, which boasted former US vice president Dan Quayle among its directors, had inside information.

"I think you are advancing the theory of a grand coincidence here - it's not," he told Mr Ross.

The Independent TD added: "Obviously your integrity is not in question, nobody questions that at all but on this deal you have done the taxpayer no service at all and you should be making a victim impact statement."

Nama also offered an insight into the scale of the loans and assets remaining on its books.

It is in the process of selling Project Arrow with bids expected by October 12.

The portfolio has a face value of 6.3 billion euro and the reserve price has been set at more than one billion euro for loans linked to property which is stated to be 50% residential.

Nama has another 14.4 billion euro of assets remaining on its books with half of that value in Dublin.

Some three billion euro worth of the property linked loans are in Co Dublin, Cork, Limerick and Galway and another 2.2 billion euro in London.

Nama also has control over 800 million euro worth of property assets around the world, mainly in Germany, France and Portugal and about 800 million euro in the UK outside of London.

Nama also rebutted further allegations made by Mr Wallace that a company was approached with the offer to pay an official a 30,000 euro bribe to exit the debt agency.

The Independent TD had claimed in the Dail that one payment of 15,000 euro was expected from the firm to arrange the relief and another 15,000 euro after the exit had been secured.

Mr McDonagh said the Garda were investigating.

"The company that's been named to me that was supposed to be involved is still in Nama, owes its full debts to Nama, did not have its debts written off," he said.

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